Sounds like a long PMS.
I used to be like this. Cramping, upset tummy constipation, water retention.For 2 weeks before my period, then I would start and have diarrhea. So frustrating.
You will have to pay attention to what exactly her intake is. Since it is summer, lots of fresh raw fruits and vegetables. Have her stay away from binders like rice, bananas white bread(hot dog and hamburger buns) pasta.
If she eats bread, find one with bran or whole wheat.
Have her increase her fluids, soda and caffeinated or diet drinks are a no,no. These will only add to the water gain and the constipation.
Make sure she is out side riding her bike or running. She needs her body to move to get all of that loose.
If it has been ore than 2 weeks , you may want her to see a doctor to make sure there is nothing else going on. Check her temperature and make sure she is not running a low grade fever, could be appendicitis.